nanoid@3.3.18 (bundled dependency) is vulnerable to CVE-2026-67214 (no fix on 3.x line) #2131

Summary

postcss currently depends on nanoid@^3.3.17 (per lib/input.js, lib/map-generator.js) via CommonJS require(). The installed 3.3.18 resolves CVE-2026-67213 (zero-size infinite loop) but remains vulnerable to CVE-2026-67214 (negative-size infinite loop), because the upstream fix (ai/nanoid#601, commit e835c9b) has only been released as nanoid@5.1.16 — no 3.x backport exists upstream.

• CVE-2026-67213: GHSA-2v37-7h3g-55p8 (fixed in 3.3.17 / 5.1.6)
• CVE-2026-67214: GHSA-28wg-ghj8-5hjv (fixed only in 5.1.16, no 3.x tag)

Why this affects postcss users

postcss cannot currently adopt nanoid@5.x because it's ESM-only, and lib/input.js / lib/map-generator.js load it via require('nanoid/non-secure'), which throws ERR_REQUIRE_ESM. This traps consumers: staying on 3.x carries an unpatched CVE; forcing 5.x breaks the build.

Requested fix (either would resolve this)

1. Request/track an upstream 3.x backport of the negative-size fix in ai/nanoid (issue: https://github.com/ai/nanoid — the fix is a one-line change, see commit e835c9b71eab832bc6106944bdd26ea96cf2c66d), or
2. Migrate postcss's internal nanoid usage from require() to a dynamic import() (or lazy-load pattern) so postcss can adopt nanoid@5.x going forward.

Environment

postcss 8.5.26, Node.js (CJS context), nanoid 3.3.18 resolved via yarn resolutions.

Happy to help test a patch if useful.